Nominally identical IC packages are typically arranged in multiple arrays on a common panel. FIG. 1 shows by way of example a panel 2 of which eighty IC packages 4 are arranged in four quadrants 6 of twenty IC packages each. (The “X” mark across each of three of the IC packages represents a defect indication made in accordance with the invention and forms no part of the prior art.) A typical panel is a multi-layer structure composed of a resin-based material, such as ABF, and patterned layers of an electrically conductive material, such as copper. Laser drilling forms a blind via in the ABF material to a depth at which a copper layer is present to enable formation of a via interconnect between different layers of an IC package. (In a subsequent step, copper in a gaseous state plates the holes to complete the interconnect.)
The state of the art in laser drilling is to stop a laser drilling process promptly upon detection of an error occurring during drilling. After drilling has been stopped, an operator removes and discards the entire panel on which the drilling error appears in typically only several IC packages. The reason for discarding the entire panel is that there is no currently available way to identify where on the panel an error has occurred. The present invention substantially reduces the number of IC packages that are unaffected by a drilling error but are rendered as scrap because of their presence on a discarded panel on which a recoverable error had occurred somewhere. A recoverable error is an error after the occurrence of which a laser drilling system could still continue processing.